Reference ranges for thyroid hormones in normal Italian children and adolescents and overweight adolescents.

BACKGROUND

As thyroid hormones are essential for normal pubertal growth and sexual development, TSH, free T₃ (FT₃) and free T₄ (FT₄) levels undergo progressive modification during childhood and puberty.

AIM

To establish thyroid hormone reference ranges in pre-pubertal children, pubertal adolescents, and adults and to evaluate any differences in thyroid function between overweight and normalweight pubertal subjects.

SUBJECTS AND METHODS

Chemiluminescent microparticle immunoassay was used to analyze TSH, FT₃ and FT₄ concentrations in serum samples from 508 children and adolescents aged 6 to 18 yr and 100 healthy adults aged 30 to 60 yr, and from 68 overweight pubertal adolescents. As data were not normally distributed, we compared them through non-parametric tests for independent samples and the reference ranges were assumed to lie between the 2.5th and 97.5th percentile.

RESULTS

We found a progressive and significant reduction in TSH, FT₃, and FT₄ levels in the three groups with increasing age. TSH levels were significantly higher in overweight patients than in the normal-weight group, but there were no significant differences for FT₃ or FT₄.

CONCLUSIONS

This study revealed significant differences in levels of thyroid hormone between different age groups and allowed us to establish normal reference ranges for pre-pubertal children between 0.87-5.19 mIU/l for TSH, 4.75-8.59 pmol/l for FT₃, and 13.09-20.61 pmol/l for FT₄, and for pubertal adolescents between 0.76- 4.51 mIU/l for TSH, 4.26-8.46 pmol/l for FT₃ and 10.94-19.09 pmol/l for FT₄.